Method for performing a cell change procedure in a wireless communication system and a device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for performing a cell change procedure in the wireless communication system, the method comprising: receiving configuration information indicating an identifier of a radio bearer to which a cell change procedure be performed; and performing the cell change procedure in RLC (Radio Link Control) and PDCP (Packet Data Convergence Protocol) entities of the radio bearer indicated in the configuration information, wherein the cell change procedure comprises a re-establishment of the RLC and PDCP entities.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for performing a cell change procedureand a device therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Although wireless communication technology has been developed to LTEbased on wideband code division multiple access (WCDMA), the demands andexpectations of users and service providers are on the rise. Inaddition, considering other radio access technologies under development,new technological evolution is required to secure high competitivenessin the future. Decrease in cost per bit, increase in serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, and the likeare required.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and device for performing a cell change procedure in a wirelesscommunication system. The technical problems solved by the presentinvention are not limited to the above technical problems and thoseskilled in the art may understand other technical problems from thefollowing description.

Technical Solution

The object of the present invention can be achieved by providing amethod for operating by an user equipment (UE) in wireless communicationsystem, the method comprising; receiving configuration informationindicating an identifier of a radio bearer to which a cell changeprocedure to be performed; and performing the cell change procedure inRLC (Radio Link Control) and PDCP (Packet Data Convergence Protocol)entities of the radio bearer indicated in the configuration information,wherein the cell change procedure comprises a re-establishment of theRLC and PDCP entities.

In another aspect of the present invention, provided herein is a UE(User Equipment) in the wireless communication system, the UEcomprising: an RF (Radio Frequency) module; and a processor to controlthe RF module, wherein the processor configured to receive configurationinformation indicating an identifier of a radio bearer to which a cellchange procedure be performed and to perform the cell change procedurein RLC (Radio Link Control) and PDCP (Packet Data Convergence Protocol)entities of the radio bearer indicated in the configuration information,wherein the cell change procedure comprises a re-establishment of theRLC and PDCP entities.

Preferably, the configuration information is indicated by the first basestation on a first type cell or a second base station on a second typecell.

Preferably, the configuration information is received through a RRCsignaling message.

Preferably, the PDCP entity does not change a security key when there-establishment of the PDCP entity is performed.

Preferably, the RLC entity is released after the re-establishment of theRLC entity is performed.

Preferably, the method further comprises transmitting a PDCP statusreport when the RLC entity is added, changed or released.

Preferably, the PDCP status report informs that which PDCP SDUs werecorrectly received and which were not correctly received.

Preferably, a PDCP entity of the radio bearer and a RLC entity in anetwork side of the radio bearer reside on different base station.

Preferably, a RRC entity of the UE requests the PDCP entity to performthe re-establishment of the PDCP entity without changing a security key.

Preferably, a RRC entity of the UE requests the RLC entity to releaseafter the re-establishment of the RLC entity is performed.

Advantageous Effects

According to the present invention, a cell change procedure can beefficiently performed in a wireless communication system. Specifically,a re-establishment of RLC (Radio Link Control) and PDCP (Packet DataConvergence Protocol) entities of the radio bearer can be efficientlyperformed in the cell change procedure.

It will be appreciated by persons skilled in the art that that theeffects achieved by the present invention are not limited to what hasbeen particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in anE-UMTS system;

FIG. 5 is a conceptual diagram for dual connectivity between a macrocell and a small cell;

FIG. 6 is a conceptual diagram for cell changing in a dual connectivitysystem;

FIG. 7 is a conceptual diagram for re-establishing RLC entity and PDCPentity in a handover procedure;

FIG. 8 is a conceptual diagram for re-establishing RLC entity and PDCPentity in a cell change according to embodiments of the presentinvention;

FIG. 9 is a conceptual diagram for performing a cell change according toembodiments of the present invention; and

FIG. 10 is a block diagram of a communication apparatus according to anembodiment of the present invention.

BEST MODE

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC. As illustrated, eNodeB 20 may perform functions ofselection for gateway 30, routing toward the gateway during a RadioResource Control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of Broadcast Channel (BCCH)information, dynamic allocation of resources to UEs 10 in both uplinkand downlink, configuration and provisioning of eNodeB measurements,radio bearer control, radio admission control (RAC), and connectionmobility control in LTE ACTIVE state. In the EPC, and as noted above,gateway 30 may perform functions of paging origination, LTE-IDLE statemanagement, ciphering of the user plane, System Architecture Evolution(SAE) bearer control, and ciphering and integrity protection ofNon-Access Stratum (NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a conceptual diagram for dual connectivity between a macrocell and a small cell.

In the next system of LTE-A, a plurality of small cells (e.g., microcell) may be present in a big cell (e.g. macro cell) having largercoverage than the small cells for optimization of data traffic, etc. Forexample, a macro cell and a micro cell may be combined for one userequipment (e.g. the dual connectivity). If the macro cell is used formanaging mobility of the UE mainly (e.g. PCell) and the micro cell isused for boosting throughput mainly in this situation (e.g. SCell), theplurality of cells combined to the UE have different coverage eachother. And each of cells can be managed by each of base stations. Thebase stations are geographically separated (inter-site CA).

The dual connectivity means that the UE can be connected to both themacro cell and the small cell at the same time. With dual connectivity,some of the data radio bearers (DRBs) can be offloaded to the small cellto provide high throughput while keeping scheduling radio bearers (SRBs)or other DRBs in the macro cell to reduce the handover possibility. Themacro cell is operated by MeNB (Macro cell eNB) via the frequency of f1,and the small cell is operated by SeNB (Small cell eNB) via thefrequency of f2. The frequency f1 and f2 may be equal. The backhaulinterface between MeNB and SeNB is non-ideal, which means that there isconsiderable delay in the backhaul and therefore the centralizedscheduling in one node is not possible.

To benefit from the dual connectivity, the best-effort traffic which isdelay tolerant is offloaded to small cell while the other traffic, e.g.SRBs or real-time traffic, is still serviced by the macro cell.

FIG. 6 is a conceptual diagram for performing a cell change procedure ina dual connectivity system.

The UE performs cell change procedure in RLC and PDCP entities when acell is added, changed, or removed. More specially, when a certain radiobearer supporting the cell is added, changed, or removed, the UEperforms the cell change procedure.

In the dual connectivity system between a macro cell and a small cell,when the small cell is added, changed, or removed, the UE performs smallcell change (SCC) procedure in RLC and PDCP entities being communicatingwith a macro base station (MeNB). The small cell (e.g., a pico-cell, afemto-cell, etc.) can be a cell having a smaller coverage than coverageof the serving cell (e.g. macro cell). The macro base station (MeNB) isone of base stations on the macro cell coverage and serves the macrocell coverage. The small base station (SeNB) is one of base stations onthe small cell coverage and serves the small cell coverage. The coverageof macro cell and the coverage of small cell have an area overlappingeach other.

When the UE performs the SCC procedure, the radio bearer whose allentities of the network may reside on a small cell or only for the radiobearer whose RLC/MAC/PHY (or only RLC entity) of the network may bemoved from the MeNB to the SeNB, from a SeNB 1 to another SeNB 2, orfrom the SeNB to the MeNB. The PDCP entity may reside on a changed cell(split bearer structure).

As shown in FIG. 6, in case of (a), when the UE connected to the MeNBmoves to the area under the SeNB1, some of the DRBs, e.g. BE-DRB (BestEffort—DRB), can be offloaded to the SeNB1. In this manner, theRLC/MAC/PHY of the BE-DRB is changed from the MeNB to the SeNB1 whilethe PDCP entity is still maintained in the MeNB.

In case of (b), when the UE connected to the MeNB moves from the areaunder the SeNB1 to the area under the SeNB2, the BE-DRB served by theSeNB1 is moved to the SeNB2. In this manner, the RLC/MAC/PHY of theBE-DRB is changed from the SeNB1 to the SeNB2 while the PDCP entity isstill maintained in the MeNB.

In case of (c), when the UE connected to the MeNB moves out of the areaunder the SeNB2, the BE-DRB served by the SeNB2 is moved to the MeNB. Inthis manner, the RLC/MAC/PHY of the BE-DRB is changed from the MeNB tothe SeNB2 while the PDCP is still maintained in the MeNB.

FIG. 7 is a conceptual diagram for re-establishing RLC entity and PDCPentity in a handover procedure.

The PDCP entity and RLC entity are re-established during handover. TheUE initiates the handover procedure when it receives aRRCConnectionReconfiguration message including mobilityControlInfoinformation element from the base station.

The UE may reset MAC and re-establish PDCP entity for all RBs (radiobearers) that are established. The handling of the radio bearers afterthe successful completion of the PDCP re-establishment, e.g. there-transmission of unacknowledged PDCP SDUs (as well as the associatedstatus reporting) and the handling of the SN (sequence number) and theHEN (hyper frame number).

The UE may re-establish RLC entity for all RBs (radio bearers) that areestablished. The UE may configure lower layers to consider the SCells(secondary cell), if configured, to be in deactivated state and applythe value of the newUE-Identity as the C-RNTI.

The UE may configure lower layers to apply the integrity protectionalgorithm and the K_(RRCint) key, i.e. the integrity protectionconfiguration shall be applied to all subsequent messages received andsent by the UE, including the message used to indicate the successfulcompletion of the procedure. The UE may configure lower layers to applythe ciphering algorithm, the K_(RRCenc) key and the K_(UPenc) key, i.e.the ciphering configuration shall be applied to all subsequent messagesreceived and sent by the UE, including the message used to indicate thesuccessful completion of the procedure.

If the UE connected as the RN, the UE may configure lower layers toapply the integrity protection algorithm and the K_(UPint) key, forcurrent or subsequently established DRBs that are configured to applyintegrity protection.

The PDCP Re-Establishment Procedure

When upper layers request a PDCP re-establishment, the UE mayadditionally perform once the procedures described in this section forthe corresponding RLC mode. The PDCP re-establishment procedurecomprises a case of UL data transfer procedures and a case of DL datatransfer procedures.

In case of UL data transfer procedures for DRBs mapped on RLC AM, whenupper layers request a PDCP re-establishment, the UE may reset theheader compression protocol for uplink and start with an IR state inU-mode. If the UE connected as an RN, the UE may apply the integrityprotection algorithm and key provided by upper layers (if configured)during the re-establishment procedure. The UE may apply the cipheringalgorithm and key provided by upper layers during the re-establishmentprocedure. From the first PDCP SDU for which the successful delivery ofthe corresponding PDCP PDU has not been confirmed by lower layers, theUE may perform retransmission or transmission of all the PDCP SDUsalready associated with PDCP SNs in ascending order of the COUNT valuesassociated to the PDCP SDU prior to the PDCP re-establishment asspecified below: i) performing header compression of the PDCP SDU ii) ifconnected as an RN, performing integrity protection of the PDCP SDUusing the COUNT value associated with this PDCP SDU iii) performingciphering of the PDCP SDU using the COUNT value associated with thisPDCP SDU iv) submitting the resulting PDCP Data PDU to lower layer.

In case of UL data transfer procedures for DRBs mapped on RLC UM, whenupper layers request a PDCP re-establishment, the UE may reset theheader compression protocol for uplink and start with an IR state inU-mode and if the DRB is configured with the header compression protocoland drb-ContinueROHC is not configured. The UE may set Next_PDCP_TX_SN,and TX_HFN to 0 and apply the ciphering algorithm and key provided byupper layers during the re-establishment procedure. If the UE connectedas an RN, the UE may apply the integrity protection algorithm and keyprovided by upper layers during the re-establishment procedure. For eachPDCP SDU already associated with a PDCP SN but for which a correspondingPDU has not previously been submitted to lower layers: i) consideringthe PDCP SDUs as received from upper layer, ii) performing transmissionof the PDCP SDUs in ascending order of the COUNT value associated to thePDCP SDU prior to the PDCP re-establishment without restarting thediscardTimer.

In case of UL data transfer procedures for SRBs, when upper layersrequest a PDCP re-establishment, the UE may set Next_PDCP_TX_SN, andTX_HFN to 0, discard all stored PDCP SDUs and PDCP PDUs and apply theciphering and integrity protection algorithms and keys provided by upperlayers during the re-establishment procedure.

In case of DL data transfer procedures for DRBs mapped on RLC AM, whenupper layers request a PDCP re-establishment, the UE may process thePDCP Data PDUs that are received from lower layers due to there-establishment of the lower layers. The UE may reset the headercompression protocol for downlink, and apply the ciphering algorithm andkey provided by upper layers during the re-establishment procedure. Ifthe UE connected as an RN, the UE may apply the integrity protectionalgorithm and key provided by upper layers during the re-establishmentprocedure.

In case of DL data transfer procedures for DRBs mapped on RLC UM, whenupper layers request a PDCP re-establishment, the UE may process thePDCP Data PDUs that are received from lower layers due to there-establishment of the lower layers. The UE may reset the headercompression protocol for downlink if the DRB is configured with theheader compression protocol and drb-ContinueROHC is not configured, setNext_PDCP_RX_SN, and RX_HFN to 0, apply the ciphering algorithm and keyprovided by upper layers during the re-establishment procedure. If theUE connected as an RN, the UE may apply the integrity protectionalgorithm and key provided by upper layers (if configured) during there-establishment procedure.

In case of DL data transfer procedures for SRBs, when upper layersrequest a PDCP re-establishment, the UE may discard the PDCP Data PDUsthat are received from lower layers due to the re-establishment of thelower layers, set Next_PDCP_RX_SN, and RX_HFN to 0, discard all storedPDCP SDUs and PDCP PDUs, and apply the ciphering and integrityprotection algorithms and keys provided by upper layers during there-establishment procedure.

The RLC Re-Establishment Procedure

RLC re-establishment is performed upon request by RRC, and the functionis applicable for AM, UM and TM RLC entities.

When RRC indicates that an RLC entity should be re-established, if it isa transmitting TM RLC entity, the RLC entity may discard all RLC SDUs.

If it is a receiving UM RLC entity, when possible, the RLC entity mayreassemble RLC SDUs from UMD PDUs with SN<VR(UH), remove RLC headerswhen doing so and deliver all reassembled RLC SDUs to upper layer inascending order of the RLC SN, if not delivered before and discard allremaining UMD PDUs.

If it is a transmitting UM RLC entity, the RLC entity may discard allRLC SDUs.

If it is an AM RLC entity, when possible, the RLC entity may reassembleRLC SDUs from any byte segments of AMD PDUs with SN<VR(MR) in thereceiving side, remove RLC headers when doing so and deliver allreassembled RLC SDUs to upper layer in ascending order of the RLC SN, ifnot delivered before. And the RLC entity may discard the remaining AMDPDUs and byte segments of AMD PDUs in the receiving side, discard allRLC SDUs and AMD PDUs in the transmitting side, discard all RLC controlPDUs. And then, the RLC may stop and reset all timers and reset allstate variables to their initial values.

During the handover procedure, both PDCP and RLC entities arere-established at handover in order to minimize the packet loss.However, in cases of the above three cell change procedure like FIG. 6,there is no such re-establishment because they are not considered as thehandover procedure, e.g. PDCP is still maintained in the MeNB.Therefore, there should be a special mechanism to minimize the packetloss specific to “cell change procedure” case because there may be lossof packets due to the change of RLC entities in the cell changeprocedure.

FIG. 8 is a conceptual diagram for re-establishing RLC entity and PDCPentity in a cell change procedure according to embodiments of thepresent invention.

When the UE receives this message, the RRC requests the PDCP and the RLCof the indicated radio bearers to perform the cell change procedure.Then, the requested PDCP and RLC entities perform the cell changeprocedure as follows.

The Cell Change Procedure in the RLC Entity Includes the FollowingBehavior.

If it is a transmitting TM RLC entity, the UE may discard all RLC SDUs.If it is a receiving UM RLC entity, when possible, the UE may reassembleRLC SDUs from UMD PDUs with SN<VR(UH), remove RLC headers when doing soand deliver all reassembled RLC SDUs to upper layer in ascending orderof the RLC SN, if not delivered before. And the UE may discard allremaining UMD PDUs.

If it is a transmitting UM RLC entity, the UE may discard all RLC SDUs.If it is an AM RLC entity, when possible, the UE may reassemble RLC SDUsfrom any byte segments of AMD PDUs with SN<VR(MR) in the receiving side,remove RLC headers when doing so and deliver all reassembled RLC SDUs toupper layer in ascending order of the RLC SN, if not delivered before.And the UE may discard the remaining AMD PDUs and byte segments of AMDPDUs in the receiving side, discard all RLC SDUs and AMD PDUs in thetransmitting side, discard all RLC control PDUs. And then the UE maystop and reset all timers and reset all state variables to their initialvalues.

The Cell Change Procedure in the PDCP Entity Includes the FollowingBehavior.

In case of PDCP transmitting side procedure for DRBs mapped on RLC AM,the UE may reset the header compression protocol for uplink and startwith an IR state in U-mode. From the first PDCP SDU for which thesuccessful delivery of the corresponding PDCP PDU has not been confirmedby lower layers, the UE may perform retransmission or transmission ofall the PDCP SDUs already associated with PDCP SNs in ascending order ofthe COUNT values associated to the PDCP SDU prior to the PDCP of thecell change procedure as specified below: i) performing headercompression of the PDCP SDU, ii) performing ciphering of the PDCP SDUusing the COUNT value associated with this PDCP and iii) submitting theresulting PDCP Data PDU to lower layer.

In case of PDCP transmitting side procedure for DRBs mapped on RLC UM,the UE may reset the header compression protocol for uplink and startwith an IR state in U-mode if the DRB is configured with the headercompression protocol and drb-ContinueROHC is not configured. The UE mayset Next_PDCP_TX_SN, and TX_HFN to 0. For each PDCP SDU alreadyassociated with a PDCP SN but for which a corresponding PDU has notpreviously been submitted to lower layers, the UE may consider the PDCPSDUs as received from upper layer and perform transmission of the PDCPSDUs in ascending order of the COUNT value associated to the PDCP SDUprior to the PDCP of the cell change procedure, without restarting thediscardTimer.

In case of PDCP transmitting side procedure for SRBs, the UE may setNext_PDCP_TX_SN, and TX_HFN to 0 and discard all stored PDCP SDUs andPDCP PDUs.

In case of PDCP receiving side procedure for DRBs mapped on RLC AM, theUE may process the PDCP Data PDUs that are received from lower layersdue to the RLC of cell change procedure. If received PDCPSN−Last_Submitted_PDCP_RX_SN>Reordering_Window or0<=Last_Submitted_PDCP_RX_SN−received PDCP SN<Reordering_Window, and ifreceived PDCP SN>Next_PDCP_RX_SN, the UE may decipher the PDCP PDU,using COUNT based on RX_HFN−1 and the received PDCP SN or decipher thePDCP PDU, using COUNT based on RX_HFN and the received PDCP SN. And thenthe UE may perform header decompression and discard this PDCP SDU.

Else if Next_PDCP_RX_SN−received PDCP SN>Reordering_Window, the UE mayincrement RX_HFN by one, use COUNT based on RX_HFN and the received PDCPSN for deciphering the PDCP PDU and set Next_PDCP_RX_SN to the receivedPDCP SN+1.

If the UE received PDCP SN−Next_PDCP_RX_SN>=Reordering_Window, the UEmay use COUNT based on RX_HFN−1 and the received PDCP SN for decipheringthe PDCP PDU.

If the UE received PDCP SN>−Next_PDCP_RX_SN, the UE may use COUNT basedon RX_HFN and the received PDCP SN for deciphering the PDCP PDU, setNext_PDCP_RX_SN to the received PDCP SN+1. And if Next_PDCP_RX_SN islarger than Maximum PDCP_SN, the UE may set Next_PDCP_RX_SN to 0 andincrement RX_HFN by one. If received PDCP SN<Next_PDCP_RX_SN, the UE mayuse COUNT based on RX_HFN and the received PDCP SN for deciphering thePDCP PDU. If the PDCP PDU has not been discarded in the above, the UEperform deciphering and header decompression (if configured) for thePDCP PDU. And if a PDCP SDU with the same PDCP SN is stored, the UE maydiscard this PDCP SDU or store the PDCP SDU.

If the PDCP PDU received by PDCP is not due to the RLC SCC procedure,the UE may deliver to upper layers in ascending order of the associatedCOUNT value. All stored PDCP SDU(s) with an associated COUNT value lessthan the COUNT value associated with the received PDCP SDU or all storedPDCP SDU(s) with consecutively associated COUNT value(s) starting fromthe COUNT value associated with the received PDCP SDU. The UE may setLast_Submitted_PDCP_RX_SN to the PDCP SN of the last PDCP SDU deliveredto upper layers. If received PDCP SN=Last_Submitted_PDCP_RX_SN+1 orreceived PDCP SN=Last_Submitted_PDCP_RX_SN−Maximum PDCP_SN, the UE maydeliver to upper layers in ascending order of the associated COUNT valueand all stored PDCP SDU(s) with consecutively associated COUNT value(s)starting from the COUNT value associated with the received PDCP SDU. TheUE may set. Last_Submitted_PDCP_RX_SN to the PDCP SN of the last PDCPSDU delivered to upper layers. And then, the UE may reset the headercompression protocol for downlink.

In case of PDCP receiving side procedure for DRBs mapped on RLC UM, theUE may process the PDCP Data PDUs that are received from lower layersdue to RLC of the cell change procedure.

If received PDCP SN<Next_PDCP_RX_SN, the UE may increment RX_HFN by one.The UE may decipher the PDCP Data PDU using COUNT based on RX_HFN andthe received PDCP SN, set Next_PDCP_RX_SN to the received PDCP SN+1. IfNext_PDCP_RX_SN>Maximum PDCP SN, the UE may set Next_PDCP_RX_SN to 0,and increment RX_HFN by one. The UE may perform header decompression (ifconfigured) of the deciphered PDCP Data PDU and deliver the resultingPDCP SDU to upper layer. The UE may reset the header compressionprotocol for downlink if the DRB is configured with the headercompression protocol and drb-ContinueROHC is not configured and setNext_PDCP_RX_SN, and RX_HFN to 0.

In case of PDCP receiving side procedure for SRBs, the UE may discardthe PDCP Data PDUs that are received from lower layers due to the RLCSCC procedure, set Next_PDCP_RX_SN, and RX_HFN to 0 and discard allstored PDCP SDUs and PDCP PDUs.

The RLC and PDCP entities in the network side also perform the abovebehaviors at the cell change procedure. The PDCP of cell changeprocedure is performed by the PDCP entity in the MeNB. But the RLC ofcell change procedure is performed by the RLC entity in the old basestation that will be removed (or not used) after the cell changeprocedure performed. For example, if the path of a DRB is changed fromthe MeNB to a SeNB, the RLC entity in the MeNB may perform the above RLCof cell change procedure, and then is removed.

The cell change procedure can be seen as a modified re-establishmentprocedure. The difference is that the Security Key is not changed in thePDCP of cell change procedure while it is changed in the PDCPre-establishment procedure, and the RLC entity is removed after the RLCSCC procedure but it is maintained after the RLC re-establishmentprocedure. Therefore, the RRC can request the PDCP to perform there-establishment procedure without applying the new Security Key, andrequest the RLC to perform the re-establishment procedure and thenrelease.

After the cell change procedure is performed, the PDCP receiving sidetransmits PDCP status report to the PDCP transmitting side to informthat which PDCP SDUs were correctly received and which were notcorrectly received. It means that the PDCP status report is triggered bythe cell change procedure. When the PDCP transmitting side receives thePDCP status report, the PDCP transmitting side retransmits the PDCP SDUsthat have not been correctly received by the PDCP receiving side.

FIG. 9 is a conceptual diagram for performing a cell change procedureaccording to embodiments of the present invention.

The UE receives configuration information indicating an identifier of aradio bearer to which the cell change procedure to be performed (S901).The cell change procedure is performed when the serving cell needs tooffload data to a target cell during connecting with the UE.

Desirably, the serving cell may indicate a request of performing thecell change procedure using a certain indicator. Or, the UE may performthe cell change procedure itself when a certain condition is met.

The configuration information may be indicated by the macro base stationon a macro cell or a small base station on a small cell. The small cell(e.g., a pico-cell, a femto-cell, etc.) can be a cell having a smallercoverage than coverage of the serving cell (e.g. macro cell). The macrobase station (MeNB) is one of base stations on the macro cell coverageand serves the macro cell coverage. The small base station (SeNB) is oneof base stations on the small cell coverage and serves the small cellcoverage. The coverage of macro cell and the coverage of small cell havean area overlapping each other. The configuration information isreceived through RRC signaling message. When the UE receives theconfiguration information, the UE may perform the cell change procedurein RLC (Radio Link Control) and PDCP (Packet Data Convergence Protocol)entities of the radio bearer indicated in the configuration information(S903˜S905). The cell change procedure may comprise a re-establishmentof the RLC and PDCP entities.

Desirably, in case of the re-establishment of the RLC entity (S903), theUE may release the RLC entity after the re-establishment of the RLCentity is performed.

Desirably, in case of the re-establishment of the PDCP entity (S905),the UE may performed the re-establishment of the PDCP entity in themacro base station the re-establishment of the PDCP entity is performedwithout applying a new security key.

The UE transmits a PDCP status report when the RLC entity is added,changed or released (S907). When upper layers request a PDCPre-establishment, for radio bearers that are mapped on RLC AM, if theradio bearer is configured by upper layers to send a PDCP status reportin the uplink, the UE may compile a status report as indicated belowafter processing the PDCP Data PDUs that are received from lower layersdue to the re-establishment of the lower layers, and submit it to lowerlayers as the first PDCP PDU for the transmission by setting the FMSfield to the PDCP SN of the first missing PDCP SDU.

If there is at least one out-of-sequence PDCP SDU stored, the UE maysubmit it to lower layers as the first PDCP PDU for the transmission byallocating a Bitmap field of length in bits equal to the number of PDCPSNs from and not including the first missing PDCP SDU up to andincluding the last out-of-sequence PDCP SDUs, rounded up to the nextmultiple of 8, the PDCP report may set as ‘0’ in the correspondingposition in the bitmap field for all PDCP SDUs that have not beenreceived as indicated by lower layers, and optionally PDCP SDUs forwhich decompression have failed, and indicating in the bitmap field as‘1’ for all other PDCP SDUs.

FIG. 10 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 10 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 10, the apparatus may comprises a DSP/microprocessor(110) and RF module (transceiver; 135). The DSP/microprocessor (110) iselectrically connected with the transceiver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 10 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 10 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

1-20. (canceled)
 21. A method for a user equipment (UE) performing acell change procedure in a communication system supporting dualconnectivity, the method comprising: receiving configuration informationfor the cell change procedure through a RRC (Radio Resource Control)message, wherein the configuration information comprises an identifierof a radio bearer of the UE and information on whether the UE is toperform reestablishment of a PDCP (Packet Data Convergence Protocol)entity or not for the radio bearer; and performing data recovery of thePDCP entity for the radio bearer, when the configuration informationindicates the UE is not to perform the reestablishment of the PDCPentity for the radio bearer.
 22. The method of claim 21, furthercomprising: performing the reestablishment of the PDCP entity for theradio bearer including configuring security keys, when the configurationinformation indicates the UE is to perform the reestablishment of thePDCP entity for the radio bearer.
 23. The method of claim 21, whereinsecurity keys of the radio bearer are not changed, when theconfiguration information indicates the UE is not to perform thereestablishment of the PDCP entity for the radio bearer.
 24. The methodof claim 21, wherein the radio bearer corresponds to a first type radiobearer established such that a radio protocol of the first type radiobearer is located in either a master base station or a secondary basestation, when the configuration information indicates the UE is toperform the reestablishment of the PDCP entity for the radio bearer. 25.The method of claim 21, wherein the radio bearer corresponds to a secondtype radio bearer established such that a radio protocol of the secondtype radio bearer is located in both a master base station and asecondary base station, when the configuration information indicates theUE is not to perform the reestablishment of the PDCP entity for theradio bearer.
 26. A user equipment (UE) performing a cell changeprocedure in a communication system supporting dual connectivity, the UEcomprising: a transceiver configured to receive configurationinformation for the cell change procedure through a RRC (Radio ResourceControl) message; and a processor connected to the transceiver andconfigured to process the received configuration information such thatthe processor identifies a radio bearer of the UE based on an identifierof the radio bearer of the configuration information and identifiesinformation of the configuration information on whether the UE is toperform reestablishment of a PDCP (Packet Data Convergence Protocol)entity or not for the radio bearer, wherein the processor performs datarecovery of the PDCP entity for the radio bearer, when the configurationinformation indicates the UE is not to perform the reestablishment ofthe PDCP entity for the radio bearer.
 27. The UE of claim 26, whereinthe processor performs the reestablishment of the PDCP entity for theradio bearer including configuring security keys, when the configurationinformation indicates the UE is to perform the reestablishment of thePDCP entity for the radio bearer.
 28. The UE of claim 26, wherein theprocessor does not change security keys of the radio bearer, when theconfiguration information indicates the UE is not to perform thereestablishment of the PDCP entity for the second type radio bearer. 29.The UE of claim 26, wherein the radio bearer corresponds to a first typeradio bearer established such that a radio protocol of the first typeradio bearer is located in either a master base station or a secondarybase station, when the configuration information indicates the UE is toperform the reestablishment of the PDCP entity for the radio bearer. 30.The UE of claim 26, wherein the radio bearer corresponds to a secondtype bearer established such that a radio protocol of the second typeradio bearer is located in both a master base station and a secondarybase station, when the configuration information indicates the UE is notto perform the reestablishment of the PDCP entity for the radio bearer.31. A method for network instructing a cell change procedure to a userequipment (UE) in a communication system supporting dual connectivity,the method comprising: constructing configuration information for thecell change procedure comprising an identifier of a radio bearer of theUE and information on whether the UE is to perform reestablishment of aPDCP (Packet Data Convergence Protocol) entity or not for the radiobearer, wherein the configuration information instructs the UE toperform data recovery of the PDCP entity for the radio bearer, when theconfiguration information indicates the UE is not to perform thereestablishment of the PDCP entity for the radio bearer; andtransmitting the constructed configuration information through a RRC(Radio Resource Control) message.
 32. The method of claim 31, whereinthe configuration information instructs the UE to perform thereestablishment of the PDCP entity for the radio bearer includingconfiguring security keys, when the configuration information indicatesthe UE is to perform the reestablishment of the PDCP entity for theradio bearer.
 33. The method of claim 31, wherein security keys of theradio bearer are not changed, when the configuration informationindicates the UE is not to perform the reestablishment of the PDCPentity for the radio bearer.
 34. The method of claim 31, wherein theradio bearer corresponds to a first type radio bearer established suchthat a radio protocol of the first type radio bearer is located ineither a master base station or a secondary base station, when theconfiguration information indicates the UE is to perform thereestablishment of the PDCP entity for the radio bearer.
 35. The methodof claim 31, wherein the radio bearer corresponds to a second typebearer established such that a radio protocol of the second type radiobearer is located in both a master base station and a secondary basestation, when the configuration information indicates the UE is not toperform the reestablishment of the PDCP entity for the radio bearer. 36.A network apparatus instructing a cell change procedure to a userequipment (UE) in a communication system supporting dual connectivity,the apparatus comprising: a processor configured to constructconfiguration information for the cell change procedure comprising anidentifier of a radio bearer of the UE and information on whether the UEis to perform reestablishment of a PDCP (Packet Data ConvergenceProtocol) entity or not for the radio bearer, wherein the configurationinformation instructs the UE to perform data recovery of the PDCP entityfor the radio bearer, when the configuration information indicates theUE is not to perform the reestablishment of the PDCP entity for theradio bearer; and a transceiver connected to the processor andconfigured to transmit the constructed configuration information througha RRC (Radio Resource Control) message.
 37. The apparatus of claim 36,wherein the configuration information instructs the UE to perform thereestablishment of the PDCP entity for the radio bearer includingconfiguring security keys, when the configuration information indicatesthe UE is to perform the reestablishment of the PDCP entity for theradio bearer.
 38. The apparatus of claim 36, wherein security keys ofthe radio bearer are not changed, when the configuration informationindicates the UE is not to perform the reestablishment of the PDCPentity for the radio bearer.
 39. The apparatus of claim 36, wherein theradio bearer corresponds to a first type radio bearer established suchthat a radio protocol of the first type radio bearer is located ineither a master base station or a secondary base station, when theconfiguration information indicates the UE is to perform thereestablishment of the PDCP entity for the radio bearer.
 40. Theapparatus of claim 36, wherein the radio bearer corresponds to a secondtype bearer established such that a radio protocol of the second typeradio bearer is located in both a master base station and a secondarybase station, when the configuration information indicates the UE is notto perform the reestablishment of the PDCP entity for the radio bearer.